/*
 * Copyright (C) 2014 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.errorprone.annotations.Immutable;
import java.util.Map;

/**
 * A {@link Network} whose elements and structural relationships will never change. Instances of
 * this class may be obtained with {@link #copyOf(Network)}.
 *
 * <p>
 * See the Guava User's Guide's <a href=
 * "https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion of
 * the {@code Immutable*} types</a> for more information on the properties and guarantees provided
 * by this class.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 * @since 20.0
 */
@Beta
@Immutable(containerOf = {"N", "E"})
@SuppressWarnings("Immutable") // Extends ConfigurableNetwork but uses ImmutableMaps.
public final class ImmutableNetwork<N, E> extends ConfigurableNetwork<N, E> {

    private ImmutableNetwork(Network<N, E> network) {
        super(NetworkBuilder.from(network), getNodeConnections(network), getEdgeToReferenceNode(network));
    }

    /** Returns an immutable copy of {@code network}. */
    public static <N, E> ImmutableNetwork<N, E> copyOf(Network<N, E> network) {
        return (network instanceof ImmutableNetwork) ? (ImmutableNetwork<N, E>) network
                : new ImmutableNetwork<N, E>(network);
    }

    /**
     * Simply returns its argument.
     *
     * @deprecated no need to use this
     */
    @Deprecated
    public static <N, E> ImmutableNetwork<N, E> copyOf(ImmutableNetwork<N, E> network) {
        return checkNotNull(network);
    }

    @Override
    public ImmutableGraph<N> asGraph() {
        return new ImmutableGraph<N>(super.asGraph()); // safe because the view is effectively
                                                       // immutable
    }

    private static <N, E> Map<N, NetworkConnections<N, E>> getNodeConnections(Network<N, E> network) {
        // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will
        // have
        // whatever ordering the network's nodes do, so ImmutableSortedMap is unnecessary even if
        // the
        // input nodes are sorted.
        ImmutableMap.Builder<N, NetworkConnections<N, E>> nodeConnections = ImmutableMap.builder();
        for (N node : network.nodes()) {
            nodeConnections.put(node, connectionsOf(network, node));
        }
        return nodeConnections.build();
    }

    private static <N, E> Map<E, N> getEdgeToReferenceNode(Network<N, E> network) {
        // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will
        // have
        // whatever ordering the network's edges do, so ImmutableSortedMap is unnecessary even if
        // the
        // input edges are sorted.
        ImmutableMap.Builder<E, N> edgeToReferenceNode = ImmutableMap.builder();
        for (E edge : network.edges()) {
            edgeToReferenceNode.put(edge, network.incidentNodes(edge).nodeU());
        }
        return edgeToReferenceNode.build();
    }

    private static <N, E> NetworkConnections<N, E> connectionsOf(Network<N, E> network, N node) {
        if (network.isDirected()) {
            Map<E, N> inEdgeMap = Maps.asMap(network.inEdges(node), sourceNodeFn(network));
            Map<E, N> outEdgeMap = Maps.asMap(network.outEdges(node), targetNodeFn(network));
            int selfLoopCount = network.edgesConnecting(node, node).size();
            return network.allowsParallelEdges()
                    ? DirectedMultiNetworkConnections.ofImmutable(inEdgeMap, outEdgeMap, selfLoopCount)
                    : DirectedNetworkConnections.ofImmutable(inEdgeMap, outEdgeMap, selfLoopCount);
        } else {
            Map<E, N> incidentEdgeMap = Maps.asMap(network.incidentEdges(node), adjacentNodeFn(network, node));
            return network.allowsParallelEdges() ? UndirectedMultiNetworkConnections.ofImmutable(incidentEdgeMap)
                    : UndirectedNetworkConnections.ofImmutable(incidentEdgeMap);
        }
    }

    private static <N, E> Function<E, N> sourceNodeFn(final Network<N, E> network) {
        return new Function<E, N>() {
            @Override
            public N apply(E edge) {
                return network.incidentNodes(edge).source();
            }
        };
    }

    private static <N, E> Function<E, N> targetNodeFn(final Network<N, E> network) {
        return new Function<E, N>() {
            @Override
            public N apply(E edge) {
                return network.incidentNodes(edge).target();
            }
        };
    }

    private static <N, E> Function<E, N> adjacentNodeFn(final Network<N, E> network, final N node) {
        return new Function<E, N>() {
            @Override
            public N apply(E edge) {
                return network.incidentNodes(edge).adjacentNode(node);
            }
        };
    }
}
